1. Field of the Invention
This invention relates to an opto-magnetic recording medium capable of recording or reproducing information by a light beam being applied thereto.
2. Description of the Prior Art
As opto-magnetic recording mediums, there are known mediums having as a recording layer a polycrystal thin film such as MnBi or MnCuBi, an amorphous thin film such as GdCo, GdFe, TbFe, DyFe, GdTbFe or TbDyFe, or a single crystal thin film such as TbFeO.sub.3.
Of these thin films, the amorphous thin film has recently been considered to be excellent as the recording layer of the opto-magnetic recording meidum when the film forming property with which a thin film of a great area is made at a temperature in the vicinity of room temperature, the writing efficiency for writing signals with small opto-thermal energy and the reading-out efficiency for reading out the written signals at a good S/N ratio are taken into account. Particularly, the amorphous thin film GdTbFe has a great Kerr rotation angle and a curie point of about 150.degree. C. and is therefore suitable as the recording layer. Further, as a result of the study continued in order to improve the Kerr rotation angle, it has been found that the amorphous thin film GdTbFeCo has a sufficiently great Kerr rotation angle and permits reading-out with a good S/N ratio.
Researches have been actively carried out to progress the improvement of the characteristics of magnetic materials which are the recording layer in this manner to thereby improve the recording efficiency and the reproducing efficiency and on the other hand, to effectively utilize the applied light energy to improve the recording efficiency and the reproducing efficiency. For example, the aforementioned recording layer is provided on a light-transmitting substrate formed of plastic material or the like and the recording or reproducing light is applied from the substrate side, and an antireflection film has been provided between the substrate and the recording layer.
However, the conventional antireflection layer has often given rise to various disadvantages. That is, depending on the material forming the antireflection layer, there has occurred a disadvantage that the layer has a sufficient refractive index to perform the antireflection effect but is poor in adherence property with respect to the substrate and is thus liable to cause peel-off or crack or a disadvantage that the layer is good in adherence property but is low in refractive index and cannot provide a sufficient antireflection effect and thus, a sufficiently satisfactory anti-reflection layer has not yet been obtained.